Wisconsin Weather

Stormy Start to September for an already flooded Wisconsin

Aug 31 2018 10:00 AM CST| 0 Comments | Wisconsin | Weather Forecasting

The weather pattern over the next few days will be similar this past week, maybe a bit weaker. It will feature toughing in western north america with direct supply of gulf moisture into the region for multiple days. Pieces of energy will flow through the jet stream with daily threat for thunderstorm development. Add in an abundance of moisture, the stage is set for consecutive days of thunderstorms and locally heavy rain across Wisconsin and the Great Lakes.

Wisconsin Weather
GFS 500mb anomalies. Abnormal upper troughing in western North America. What I have labeled is a trend, not necessarily the exact position of the jet stream each day.

The 7-Day forecast for Oshkosh, Wisconsin shows precipitation chance pretty much every day. For those who follow the our blog, trough in the west means storminess in Wisconsin.

Wisconsin Weather
Oshkosh 7 Day forecast

August 2018 will end as one of the wettest in history for several Wisconsin cities across southern Wisconsin. Wish I could provide the factual records but you can take my word for it.

Half the yearly average rainfall has come overnight in some places, such as Cross Plains, WI. On August 21 Cross Plains,WI broke the record for 24hr precipitation with 15.33" overnight! Between Sunday night and Tuesday this week another 11" was measured between Vernon and Ozaukee counties in southern Wisconsin. These events alone are historic in magnitude!

Wisconsin Weather
Observed - Overall August rainfall estimates show 15"+ from Vernon to Ozaukee counties, mostly falling in the last 10 days of the month

While the flood waters have receded for most, rivers are near or above record levels. The ground is saturated so it won't take much to push things over the top again. The forecast for tonight through early next week brings heavy rains back to pretty much the same places.

Forecast thru next Saturday

Wisconsin Weather
GFS forecast. Spots will exceed 8"+ over the next five days. Nailing down exact placement of heaviest rains is not possible right now and will become clearer on a day to day basis. This model is not very good with convective thunderstorms therefore precip amounts definitely could be understated!

Heavy rain is notoriously difficult to predict due to it's localized nature. The amount of heavy rain recently has forced us to redefine how we forecast excessive heavy rain. When it comes to heavy rain and severe weather, the forecast is usually a day-to-day process. We will be approaching this on a day to day basis.

Wisconsin Weather
Three day outlook for heavy rain start with Friday on left, Saturday middle, Sunday right. These are the general areas we think might have the heaviest rains.As mentioned earlier we are using the zones to mark heaviest rain regions and not an exact forecast accumulation range prediction. Hashed zones are target areas with our best guess biggest impact at this point.

I predict the rain events will less intense but there will be more opportunities for heavy rain compared to August. It's possible that the pattern will shift slightly from what is currently forecast next week and put heaviest rain somewhere else besides the already flooded regions. At the very least this is something you should be aware of as we move forward. You can read our hazardous weather outlooks create daily here.

On the severe weather end, I don't foresee a repeat of last week's tornado outbreak or widespread threats yet due to a weaker upper level jet. This could change as details work themselves out each day. I would say heavy rain is the primary concern.

Extra Thoughts

  • The setup looks similar to a southwest US pineapple express or atmospheric river pinching into Wisconsin, similar to last week.

  • Simply based on the tendency toward heavy rain bomb events in the last six months, I'm very curious to see how the fall and winter will go. There will be some major snow events, perhaps early snows; if this trend continues. Was the Blizzard of April 2018 just the beginning?

  • Amplified jet stream patterns and heavy rain bomb events has been linked to solar/sun activity which is currently at minimum. I do expect our weather to become more extreme over the next three years. Not just heavy rain or snow but droughts, heat, cold, and other issues.

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